Low cost, low weight and high performance integrated filter banks are critical components of, e.g., advanced channelized receiver and exciter modules. These require miniaturized low-cost filter technology offering excellent performance, as well as high manufacturing yield to reduce costs.
Currently the production miniature UHF, RF, and microwave circuits, especially filters, are based on xe2x80x9clumped elementxe2x80x9d technology where lumped capacitors (xe2x80x9cCsxe2x80x9d) and inductors (xe2x80x9cLsxe2x80x9d) are used to construct a filter. Such filters are expensive due, e.g., to the extensive to tuning time needed to tune each filter. Furthermore, such filters require a relatively large foot print, a high Z dimensional height and are relatively heavy.
Another approach for filter miniaturization utilizes Lanthanum Aluminate (LaAIO3) substrates with an assumed relative dielectric constant of xcex5r=24. These types of material have in the past only been used in the growth of low temperature superconducting (xe2x80x9cLTSxe2x80x9d) films. Such substrates are expensive, suffer from a high dislocation density, and have a rather low dielectric constant, e.g., xcex5r= less than 24. They have been limited in effectiveness, e.g., to certain space applications where small cryogenic refrigeration capabilities exists, where such distributed small filters have played an important role, albeit at a considerable cost, as discussed in xe2x80x9cCompact Forward-Coupled Superconducting Microstrip Filters for Cellular Communication,xe2x80x9d IEEE Transactions on Applied Superconducting, Volume 5, No. 2, 1995, pages 2656-2659.
Current Multi-Chip-Microwave-Modules are based on Alumina, Duroid or low temperature co-fired ceramic (LTCC) material. In general, the surface morphology of known thick film metallization is not very smooth due to the rather large grain size of the conductor paste.
Complex multi-layer fabrication technology generally requires a dielectric interposer-layer, sometimes called dielectric lamination layer, either as part of the microwave/RF circuit topology or as the means of physically separating the RF conducting layers from the control DC circuitry or both. Stripline RF and microwave circuits also need a lamination layer that is electrically part of the circuit dielectric layer, meaning that such layer has to have a low loss tangent (high Q) and a consistently high dielectric constant xcex5r, e.g., greater than or equal to 100.
RF filter circuits are described which include a bottom dielectric substrate fabricated of a high dielectric material having a relative dielectric constant in a range of 30 to 100. A conductor pattern defining a circuit topology is fabricated on a surface of the substrate.